This invention relates to a process for recovering lube oil base stocks from used motor oil formulations. In particular, this invention relates to the removal of metallic additive packages from the waste oil to facilitate further processing of the used motor oil. The invention further relates to asphalt blend compositions containing used motor oil bottoms from the process, and asphalt pavement compositions containing the asphalt blend compositions.
Automotive lubricating oils are usually formulated from paraffin based petroleum distillate oils or from synthetic base lubricating oils. Lubricating oils are combined with additives such as soaps, extreme pressure (E.P.) agents, viscosity index (V.I.) improvers, antifoamants, rust inhibitors, antiwear agents, antioxidants, and polymeric dispersants to produce an engine lubricating oil of SAE 5 to SAE 60 viscosity.
After use, this oil is collected from truck and bus fleets, automobile service stations, and municipal recycling centers for reclaiming. This collected oil contains organo-metallic additives such as zinc dialkylthiophosphate from the original lubricating oil formulation, sludge formed in the engine, and water. The used oil may also contain contaminants such as waste grease, brake fluid, transmission oil, transformer oil, railroad lubricant, crude oil, antifreeze, dry cleaning fluid, degreasing solvents such as trichloroethylene, edible fats and oils, mineral acids, soot, earth and waste of unknown origin.
Reclaiming of waste oil is largely carried out by small processors using various processes tailored to the available waste oil, product demands, and local environmental considerations. Such processes at a minimum include chemical demetallizing or distillation. The presence of organo-metallics in waste oils such as zinc dialkylthiophosphate results in waste oils becoming sticky, overly viscous and thus difficult if not impossible to process. Moreover, the resulting sludge created reduces the amount of salable product, as well as creating additional disposal problems.
Successful reclaiming processes require the reduction of the organo-metallics (or ash) content to a level at which the hot oil does not become sticky. Such reduction can be carried out by chemical processes which include reacting cation phosphate or cation sulfate with the chemically bonded metal to form metallic phosphate or metallic sulfate. U.S. Pat. No. 4,432,865 to Norman, the contents of which are incorporated herein by reference, discloses contacting used motor oil with polyfunctional mineral acid and polyhydroxy compound to react with undesired contaminants to form easily removable reaction products. These chemical processes suffer from attendant disposal problems depending on the metal by-products formed.
Ash content can also be reduced by heating the used lubricating oil to decompose the organo-metallic additives. However, indirect heat exchange surfaces cannot be maintained above 400.degree. F. (204.degree. C.) for extended periods without extensive fouling and deposition of metals from the additives. Used lubricating oils can be heated to an additive decomposition temperature of 400.degree. F. (204.degree. C.) to 1000.degree. F. (538.degree. C.) by direct heat exchange by mixing with a heated product oil as disclosed in U.S. Pat. No. 5,447,628 to Harrison, et al., the contents of which are incorporated herein by reference. However, dilution of the product oil with used oil obviously suffers from the inefficiency of reprocessing already processed product oil, as well as rapid fouling of reactor surfaces. U.S. Pat. No. 4,101,414 to Kim, et al., incorporated herein by reference, discloses predistillation by steam stripping for several hours of a used lubricating oil stock in order to remove light oil, residual water, sulfur, and NO.sub.x. The temperature is kept at temperatures which avoid additive breakdown, and the process provides a concentrate product upon vacuum distillation. Flow processes using heat exchange by direct contact with hot hydrogen have been proposed but are expensive in view of the costs associated with hydrogen compression and hydrogen's low heat capacity. Such processes include UOP's Hy-Lube described in U.S. Pat. Nos. 5,244,565 and 5,302,282 which feature an initial used oil feed fractionation step to remove sludge and a majority of metals utilizing a hot circulating hydrogen stream as a heating medium to avoid deposition of decomposed organo-metallic compounds on heating surfaces, followed by a hydrotreating circuit with caustic neutralization to eliminate chlorides, with a final product fractionation step. Flow processes utilizing steam have also been proposed. However, even when used motor oil is directly heated, i.e., in the absence of heat transfer surfaces, the nozzles and downstream piping can plug in 24 to 72 hours due to the presence of organo-metallic compounds.
It would be advantageous to provide an efficient method for demetallizing used motor oil by thermal treatment using direct heat exchange in a process which does not require apparatus susceptible to clogging or fouling under the conditions encountered during decomposition of metallic additives. It would also be advantageous to provide a process for treating used motor oil which does not require preseparation of light materials or water found in used motor oil as collected.